To perform setup operations on an injection molding machine in the conventional art, a fixed mold and a movable mold fitted to each other are lifted by a crane and are mounted on a fixed platen of the mold assembly. In this case, a locating ring is used to adjust the nozzle centers of the fixed mold and fixed platen. For example, a locating ring is mounted on the fixed mold and is fitted into the locating hole provided on the fixed platen. In this case, the diameter of the locating ring is generally formed smaller than the locating hole diameter by about 30 μm. This is because a crane is used, and accurate positioning cannot be performed.
Another embodiment can be found in Patent Document 1 which discloses a mold positioning device wherein a locating ring is provided around the nozzle center of the fixed platen, and the mold is provided with a locating ring engaging hole. The apparatus of this Patent Document is claimed to ensure easy positioning of the mold into the fixed platen of the molding machine, independently of the external size of the mold.
However, the mold positioning device disclosed in Patent Document 1 also uses a mold setup method using a crane, and there is a limit to the positioning accuracy. The locating ring machining accuracy is also limited. Thus, a certain degree of clearance has to be provided between the locating ring and locating ring engaging hole. The positioning accuracy has been limited because of this clearance.
Further, the fixed platen is generally made of cast iron. Thus, when a locating hole is formed on the fixed platen, the forming accuracy and surface roughness have been difficult to improve. The mold is commonly made of a material (e.g., carbon steel) which is tougher than the fixed platen. Thus, the locating hole of the fixed platen tends to be deformed by repeated mold setup procedures. If the locating hole is deformed, the clearance with the mold is increased and the positioning accuracy is reduced. These problems have been left unsolved.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-11241